I’ve finally finished machining the slots in the end of the knurling tool arms. It’s been a slow process as each pass of the milling cutter only took of 0.5mm and I had to machine both sides of the slots

For the knurling tool I’m making I decided to attach a couple of the parts together with some countersunk screws. This raised the question of how do I ensure I’ve drilled it the right size? Conveniently in the UK the